Can anyone recommend a good soudium light filter?

In message , Simon
Gartfield writes
My site though well away from any major cities does suffer from
moderate light pollution from localised sodium light street lamps etc.

Sodium lamps come in two flavours low pressure pure yellow ones, and
high pressure peachy white ones. A quick look at their spectrum
reflected off a CD will allow you to tell them apart. The former can be
filtered out relatively easily.

I should declare an interest here, since I sell a photographic filter,
Nonad, designed to prevent yellow sky fog from low pressure sodium
lights.

http://www.nezumi.demon.co.uk/nonad/nonad.htm

And I have a few sample images with and without filtration and including
different street lamp spectra filtered by various representative LPR
filters.

I have heard mixed reviews regarding the use of light pollution
filters, and wonder can anyone recommend one which really works.

They all work, but do not expect miracles. Broadband filters in general
do not give much obvious visual contrast improvement, but are very
useful photographically. Onset of sky fog is delayed and when it
develops is a more neutral grey rather than dirty muddy brown.

Neodymium doped glass filters like Nonad are very effective in that
application provided that most of the light pollution is from LPS. And
about 45% of the UK street lighting is presently of this type.

However, the eye sees things differently. The most effective visual
Sodium filter that I have seen is the one from Orion Optics(UK) and that
is moderately effective against all sodium lights as an efficient cyan
interference filter.

Nebula filters offer still higher contrast by passing only the light
from emission nebulae and blocking everything else including most
starlight.

You should also take a look at David Knisely's filter FAQ on
sci.astro.amateur.

Don't waste your money on more expensive US broadband filters - they are
optimised for mercury street lighting environments.

Regards,
--
Martin Brown